The turbine section of a turbine engine is enclosed within an outer casing. A blade ring or vane carrier is disposed within the outer casing. One or more rows of stationary airfoils, known as vanes, can be attached to and extend radially inward from the inner periphery of the vane carrier. Depending on the engine, there may be a single vane carrier hosting every row of vanes, or there can be multiple vane carriers with each hosting at least one row of vanes.
The rows of vanes alternate with rows of rotating airfoils, commonly referred to as blades. Each row of blades is formed by a plurality of blades provided on a rotor disc such that the blades are arrayed about the periphery of the rotor disc. The individual blades include an airfoil, a platform and a root. The blade root is held in a slot provided in the disc. While the blades are held circumferentially and radially by their engagement with the slot and with the adjacent blades, such engagements do not sufficiently restrain the blades in the axial direction. Accordingly, some turbine engines include a locking system to axially retain the blades.
FIG. 1 shows a known system 10 for axially locking a blade 11. More specifically, the system 10 includes a plate 12. The plate 12 has a radially outer end 14 and a radially inner end 16. At its radially outer end 14, the plate 12 engages a slot 18 provided in the platform 20 of the blade 11. The plate 12 is secured near its radially inner end 16 to the rotor disc 22 by a bolt 23. Such locking hardware is provided on the axial upstream side 24 and the axial downstream side 26 of the disc 22 so as to substantially restrict movement of the blade 11 in the axial direction. A plurality of plates 12 can be provided about each side 24, 26 of the disc to axially restrain the entire row of blades 11.
Though successful in achieving the desired axial restraint, the prior locking hardware 10 can hinder the installation and/or removal of one or more blades 11 from the disc 22. For example, turbine inspections have revealed damage to only the last row turbine blades in some instances. The locking hardware 10 on the axial downstream side 26 of the disc 22 can be accessed and removed through the engine exhaust (not shown); however, the locking hardware 10 on the axial upstream side 24 of the disc 22 is not readily accessible. In order to remove the axial upstream locking hardware 10 and the blades 11 themselves, the outer casing (not shown) and the vane carrier (not shown) surrounding the last row of blades must be removed to gain access to the axial upstream locking hardware 10, particularly the bolt 23.
The removal of the outer casing and the vane carrier can require, among other things, the mobilization of a crane, special tooling, and work crews for additional work shifts. The expenses associated with such an undertaking can be considerable. Moreover, such a project can result in extended outages, and some service contracts can provide for significant liquidated damages or other penalties for extended outages. Thus, there is a need for an turbine blade axial locking system that can facilitate the installation and removal of turbine blades.